1. Field of the Invention
The present invention relates to a mold for production of a thermoplastic resin molded article having a hollow part, and a process for production of a thermoplastic resin molded article having a hollow part using the same mold. Hereinafter, a hollow thermoplastic resin molded article and a thermoplastic resin are referred to as xe2x80x9chollow molded articlexe2x80x9d and xe2x80x9cresinxe2x80x9d, respectively.
2. Description of Related Art
Hollow molded articles have been produced, for example, by feeding molten resin into a cavity of a mold, provided with a movable or fixed gas introducing pin, as shown in FIG. 16, and directly introducing compressed air or high-pressure gas into the molten resin through a tip of the gas introducing pin which protrudes into the cavity (see, for example, JP-A 3-164222 and JP-A 5-16177).
However, the mold used in this method is costly due to the presence of the gas introducing pin and the design of the mold is restricted due to the larger space occupied by the gas introducing member in the mold. In addition, since a gas-ejecting hole of the gas introducing pin is easily choked with resin, maintenance of the gas introducing pin is costly and time consuming. In addition, a trace formed by pulling out the gas introducing pin after molding remains on the surface of the hollow molded articles produced by this method. Further, choking of the gas-ejecting hole with resin prevents gas introduction, which decreases the amount of introduced gas and leads to formation of an insufficient hollow part.
The object of the present invention is to provide a mold which can successfully form a hollow part in the interior of a thermoplastic resin molded article and yield a hollow molded article having a good appearance and a process for production of a hollow molded article using the same mold.
This object as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.
The present invention provides a mold for production of a hollow molded article which includes a pair of a female and a male mold members, wherein a gas passage is provided in either of the female or the male mold member, and a gas introducing member for introducing a gas into a cavity formed between the female and the male mold members is provided in communication with the gas passage such that a tip of the gas introducing member does not protrude into the cavity. The gas introducing member has a gas path which is open at its tip and is in communication with the gas passage in the mold. In the mold of the present invention, the gas introducing member is provided such that its tip does not protrude into the cavity. Thus, the above problems related to molds employing a gas introducing pin can be overcome.
In the mold of the present invention, the gas passage provided in either of the female or the male mold member may be directly opened on a cavity plane instead of through the gas introducing member.
In addition, in the mold of the present invention, the cavity plane provided with the gas passage may be further provided with a lagging material. Upon use of such a mold, since the formation of a skin layer on a surface of a resin is prevented by the action of the lagging material, the introduction of gas into the molten resin is promoted.